GAI bat biologists conduct surveys for rare, threatened, and endangered bat species and successfully help clients to avoid, minimize, or mitigate habitat impacts to satisfy state and federal agency requirements that protect these and other wildlife living within the vicinity of proposed projects. The Indiana bat (Myotis sodalis) is one such species, with a wide distribution across the Eastern and Midwestern United States.
Indiana Bat Facts
The Indiana bat got its name because the first specimen was found in southern Indiana’s Wyandotte Cave in 1904. Presently, their habitat ranges as far west as Missouri, and across the eastern U.S. from southern New Hampshire to northern Florida. While Indiana bats are difficult to distinguish from other bat species, scientists can identify them by the smaller size of their feet and the shorter length of their toe hairs. Indiana bats help consume billions of insects each year, while also serving as pollinators and seed spreaders. The Indiana bat was originally listed as in danger of extinction under the Endangered Species Preservation Act of 1966, and is currently listed as endangered under the Endangered Species Act of 1973 (ESA).
In 2019, a census estimated 537,297 Indiana bats had been observed in 16 states—a dramatic decline of about 50% compared to when the species was first listed as endangered. This is likely attributed to many factors, including habitat destruction. Because of their instinctive behavior of hibernating in large communal groups, Indiana bats are particularly susceptible to disturbance, vandalism, or adverse modification of their winter habitat, which are called “hibernacula” and are generally composed of caves and abandoned mines. Another major threat that has emerged in recent decades is a fungal disease called white-nose syndrome (WNS). In 2021, an estimated 6.7 million bats, including Indiana bats, were reported to have been killed by WNS since the disease’s arrival in North America in 2006. Indiana bats receive protection in the form of bat-friendly gates that keep humans out of their hibernacula; however, this does little to combat WNS, since bats are the main culprits for spreading the disease.
The scientific name of Myotis (“mouse ear”) sodalis (Latin for “companion”) helps describe the physical and behavioral characteristics of this social, albeit often misunderstood, species. It is only “social” among its own kind—that is, it has a habit of clustering in large groups (as many as 500 bats per square foot) in their hibernacula during cold winter months.
Compared to other bats in the eastern U.S., the Indiana bat is on the smaller end of the size spectrum, measuring between 1.5 and 2 inches long, and weighing only about a quarter of an ounce (about the weight of a house key or a few pennies). Studies indicate that Indiana bats live 5 to 10 years on the average; however, some can live as long as 14 years.
Habits and Habitats
After several months of hibernation, the Indiana bat begins its annual spring migration to wooded or semi-wooded habitats. Male bats prefer to be alone or in very small groups; however, during summer months, pregnant Indiana bat females gather in maternity colonies of up to 100 individuals to roost and bear their young (called “pups”) under loose tree bark or in tree crevices, preferring dead trees in full sun for their warmth. Females only bear one offspring a year. At about 1 month old, each young bat is introduced to flight by soaring and swooping in tandem with its mother.
During autumn, Indiana bats congregate in caves (called swarming) to mate and to finish their summer/fall mission to accumulate life-saving fat reserves (energy) in preparation for winter hibernation. Although mating takes place during swarming, sperm is stored by females during hibernation until spring, when they will become pregnant and prepare for migrating to summer roost areas.
Utilizing their stored fat (their only energy source during hibernation), Indiana bats must wait out the winter in cool, humid caves or mines that remain above freezing. Although hibernacula with stable low temperatures (under 50°F) that allow for a reduction in metabolic rate and conservation of fat reserves are ideal, these conditions are not equally distributed across the landscape. Therefore, the bats must often travel hundreds of miles to hibernate collectively in groups that can range from a few to 50,000 or more individuals.
Rare, Threatened, and Endangered Bat Studies
GAI conducts and coordinates studies for rare, threatened, and endangered species—including bats. Across the eastern U.S., the Indiana bat is one of the most frequently encountered federally endangered species to arise during U.S. Fish and Wildlife Service (USFWS) reviews of proposed projects. Federally listed species like the Indiana bat are protected by the ESA from incurring unnecessary “take” (i.e., being killed, harmed, harassed, or otherwise negatively affected). Therefore, projects that could contain Indiana bat habitats must consider any potential effects that could arise. In support of proposed projects, GAI’s team of biologists perform environmental reviews, GIS habitat evaluations, spatial analyses, field habitat assessments, presence/absence surveys, reporting, mitigation planning, and agency coordination/consultation.
Our biologists conduct surveys and studies not only for the Indiana bat, but also for other federal- and state-listed threatened or endangered bat species. Although typically covered under the overall umbrella of Indiana bat surveys, GAI biologists must also consider other federally endangered bat species such as the gray bat (Myotis grisescens) and Virginia big-eared bat (Corynorhinus townsendii virginianus), which typically roost in caves year-round. Due to the devastating effects of WNS, the USFWS proposes to uplist the northern long-eared bat (Myotis septentrionalis) from federally threatened to federally endangered. USFWS is also proposing to list the tricolored bat (Perimyotis subflavus) as federally endangered and is currently evaluating the little brown bat (Myotis lucifugus) for the possibility of federal listing.
GAI biologists have extensive experience performing and coordinating studies for rare, threatened, and endangered bat species. Our full-time bat biologists have a combined total of nearly 50 years of experience and have managed, conducted, or volunteered on bat projects in most states across the ranges of the Indiana bat and other federally listed species.
GAI’s bat services includes a range of studies that may be involved in projects that could potentially contain suitable habitat for Indiana bats or other bat species:
- Habitat assessments
- Potential roost tree searches
- Hibernacula/portal searches
- Hibernacula/portal trapping
- Mist netting presence/absence surveys
- Acoustic presence/absence surveys
- Radio telemetry studies
- Roost tree emergence surveys
- Habitat mitigation and monitoring
- Bat Conservation Plans
- Protection and Enhancement Plans
Contact Adam Mann, 859.692.4122, Jason Duffey, 859.692.4152, or Bethany Gregory, 859.692.4133, to find out more about GAI’s Wildlife & Protected/Endangered Species services—message GAI online and start the conversation about how our multidiscipline professionals can meet your unique project needs.
References
Indiana Bats. Indiana Department of Natural Resources. Digital file accessed 10/24/2022. http://www.in.gov/dnr/fishwild/3371.htm
Indiana Bat. National Wildlife Federation. Digital file accessed 10/24/2022. https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/Bats/Indiana-Bat
Indiana Bat. U.S. Fish & Wildlife Service. Digital file accessed 10/24/2022. Indiana Bat (Myotis sodalis) | U.S. Fish & Wildlife Service (fws.gov)
Indiana Bats. What do they need? Habitat! When do they need it? Now! The Nature Conservancy, December 14, 2021. Digital file accessed 10/24/2022. https://www.nature.org/en-us/about-us/where-we-work/united-states/indiana/stories-in-indiana/indiana-bats/
